In the recent medical field, it has been eagerly desired that the amount of processing waste fluid is reduced, from the viewpoints of environmental preservation and space saving. Accordingly, techniques relating to photothermographic materials for medical diagnosis and photographic technology have been required which can be efficiently exposed with laser image setters or laser imagers and can form sharp black images having high resolution. These photothermographic materials can dispense with the use of processing chemicals of the solution family, so that they can provide to customers heat development systems which are simpler and do not damage the environment.
On the other hand, the recent rapid progress in semiconductor laser technology has made it possible to miniaturize medical image output units. Naturally, techniques of infrared-sensitive heat developable silver halide photographic materials in which semiconductor lasers can be utilized as light sources have been developed. Spectral sensitization techniques are disclosed in JP-B-3-10391 (the term "JP-B" as used herein means an "examined Japanese patent publication"), JP-B-6-52387, JP-A-5-341432 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-6-194781 and JP-A-6-301141, and further, antihalation techniques are disclosed in JP-A-7-13295 and U.S. Pat. No. 5,380,635. In light-sensitive materials based on the assumption that infrared exposure is used, the visible absorption of sensitizing dyes and antihalation dyes can be significantly decreased to easily produce substantially colorless light-sensitive materials.
Such photothermographic materials have hitherto been produced by forming light-sensitive layers comprising organic solvents such as ketones as main ingredients and thermoplastic hydrophobic polymers. However, the organic solvents are used in large amounts, which causes the occurrence of environmental problems or extremely high costs for recovery. Further, it is difficult to promote the efficiency of the production by simultaneous coating in multiple layers, resulting in high costs. Accordingly, photothermographic materials in which aqueous solvent coating is possible have been desired. Studies for making the aqueous solvent coating possible have been conducted. However, when precedence is given to the image quality, blocking is liable to occur. Further improvements have therefore been desired.